Question

Need help. How to diagnose misfire. 96 Chevy K1500.

I am considering buying a 1996 Chevy K1500 Silverado from a friend but need to figure out what the Idle / gas smell problem is first and am not sure how to go about diagnosing this.

While in drive at a stop the trucks idle drops and kind of surges, shifting into neutral brings the idle up to normal it seems.

I also think I smell the gas being a little rich perhaps. I am not very mechanically inclined but have cranked some wrenches before so I know I smell something...just not sure what.

The first place I took it said they checked the cap and rotor and since it looked fine they wanted to install a new fuel injection assembly at a cost of $900 (not gonna happen).

Second place checked the codes and said there was a random misfire and thought I should check the cap and rotor and if they are good to replace some control module for $120.

So what does someone like myself do to diagnose this? How do I trust any mechanic when I get different answers like this and don't have any extra money for "attempts" at fixes. Oh the stress I have had already, can't wait to see what happens if I buy it...lol.